As Late As Possible Constraint: How To Use It In Primavera P6 [VIDEO]

Ever been confused by Primavera P6’s As Late As Possible constraint? If you’re a still familiarizing yourself with P6’s many features, you might not be sure what the As Late As Possible constraint does or when to use it.

I had Avi ask me that question recently and decided to put this informative video together. I had a chance to practice my whiteboard skills and hopefully you’ll understand how the As Late As Possible constraint affects activities, and their Free Float in Primavera P6.

On a technical note, I was a bit disappointed with the auto whitebalance setting on my camera that led to the brightening and darkening of the video at random. But, as they say, why be perfect when good is good enough.

How do you use the As Late As Possible Constraint in Primavera P6 and what exactly does this constraint do?

Transcript:
Hey Plan Academy fans, it’s Michael back here in Plan Academy Studios with another Ask Plan Academy question. Today’s question comes from Avi. Avi is one of our members here at Plan Academy and he had some questions around how to use the “as late as possible” constraint. What exactly does the “as late as possible” constraint do? Great question. Let’s see if we can get into it.

Let’s use the whiteboard. I’ve drawn up a quick example here. I’ve got a simple network with a bunch of activities. I’ve got early dates up at the top and late dates down here at the bottom. When we apply any constraint, we know that those constraints can affect the early and late dates. And as a result, that can also affect both of our total float and free float calculations. What the “as late as possible” constraint does is it takes free float of an activity down to zero.

What’s free float? Free float is how much duration I have between an activity and its successor. Now, in a lot of cases when I have a bunch of activities string together, I have no free float here. These are all happening one after the other. But in this case because Primavera and CPM scheduling says, “Do thing as early as possible,” we’re looking at the early dates. I have seven days of free float here. That free float value also matches the total float value.

If I was going to draw this on a Gantt chart it will look something like this. I have my A activity here, my B activity here, my C activity. I know I’m not exactly to scale, but essentially D here will be schedule as early as possible – so it would be butted up against our start milestone here.

When you apply that “as late as possible” constraint, Primavera will take this activity and rescheduled it to be as late as possible, so not as early as possible but as late as possible. What will happen was D will end up over here. It is the same duration as C so we’ll just make it the same. When D ends up as late as possible, then essentially, it’s taking the free float which is that duration here between the activity and the successor and it’s setting that to zero. That activity ends up basically budding up against its successor. That’s how the “as late as possible” constraint work.

When are you going to use this? Well, there are lots of examples. Any time you have a deadline and you need some things to happen right before the deadline, you can use that “as late as possible” constraint.

Now, you want to use some scrutiny around this. This activity C here also has to happen before the deadline. But depending on the nature of the work, you may not use an “as late as possible” constraint. It’s usually used for activities that can be done any time. They don’t have to be done as early as possible. They can be done any time in that duration but maybe we want to leave it for right before that deadline.

I’ll give you an example, “clean up the work site before the deadline”. I know I can do it somewhere in here but I’ll probably going to do it right before. Okay so that’s an example.

That’s our synopsis here on “as late as possible”. Hopefully, that clears things up for you. Come on back to Plan Academy and check out more of our videos soon.

If you have a question you’d like answered, post it to our Facebook page and we will queue it up for a response in this series.

About Michael Lepage

Michael is an avid project controls blogger and is the Chief Learning Officer here at Plan Academy. Michael has taught 1000s professionals how to use project controls software like Primavera P6 over the past 10 years through his online courses and tutorials. Michael is a member of AACE, the Guild of Project Controls and holds his PMP certification from PMI.

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Comments

Schedule consultants always criticize the use of “as late as possible” constraints when evaluating baseline schedules. However, I do see some merit in using them in particular instances such as permit acquistion activities that have expiration periods. For example it is not realistic to apply for permit good for 6 months if it is not needed for another year. If the only true predecessor is NTP for this permit activity and its only true successor is a construction activity that occurs next year, then the “as late as possible” will push the early start date of the permit activity to when it will be needed instead of 1 day after NTP.

The downside of “as late as possible” constraints is if the successor activities are on the longest / critical path, then the “as late as possible” constraint will artificially make that activity critical and will show up on longest/critical path printouts.

I wish P6 had the capability of selecting certain activities for a “planned start/finish” that is neither the earliest or latest possible dates where the green bar for select activities can either be the early or the planned start/finish dates at the choice of the user. This would be helpful for short term look ahead schedules.

Thanks for the comment Rich. Probably I should have added a bit about minimizing your use of the “ALAP” constraint. In fact, now consultants are criticizing the use of any constraints and possibly that’s justified.
I advocate for limited use of ALAP in specific circumstances, when activities are not on the CP or near-critical.

ALAP constraint could be used for procurement activities, but the problem is that any activity that I applied ALAP constraint its free float now is zero. So in this circumstance, I prefer to use any lag on the relationship of its predecessor and keeping the activity out of the critical path. What do you think?
Regards,